WASHINGTON — It was well past 4 a.m., and the House was still in session. Exhausted lawmakers slumped in their seats as the debate over a $151-billion transportation package droned on.

Amid the huzzahs over jobs, economic growth and the invective over the legislation's cost, one element was missing: The 486-page bill itself was still being frantically pieced together by aides.

By the time the House passed the legislation 372-47, only a handful of lawmakers had read one word of it.

To Rep. Christopher Cox, a young Newport Beach Republican then serving his second term in Congress, the events of that late November morning two years ago represented all that is wrong with the United States Congress. Lawmakers literally were deciding the fate of tens of billions of the taxpayers' dollars on the strength of a nod and a handshake.

Two years later, Cox is thinking hard about making a move to the other side of the Capitol. He has written two letters to his financial supporters, informing them that he is planning to seek the Republican nomination for the seat held by Democrat Dianne Feinstein. Rep. Michael Huffington, a millionaire businessman from Santa Barbara, announced last week that he will seek the Republican nomination.

For the past several weeks, Cox has met with party leaders throughout California to seek advice and support. Should he decide to risk his safe congressional seat, Cox has the endorsements from two former Senate candidates--Bruce Herschensohn and Ed Zschau--as well as former President Reagan's Housing secretary, Jack Kemp.

At this pivotal point in Cox's career, his reaction to the early morning debate in 1991 serves to take his measure as both a lawmaker and politician.

A graduate of both the Harvard law and business schools, the 40-year-old Cox is described by even his critics as brilliant. He has a reputation on Capitol Hill as a button-down, economic conservative whose anti-tax, anti-spending rhetoric is highly principled, if not always politically prudent.

The transportation bill is a case in point. Even though the legislation contained $4.1 million for road work in and near Cox's own Orange County district, he voted against the bill, largely because he was incensed that the House would debate and approve such important legislation literally under the cloak of darkness.

A few weeks after the bill passed, Cox went public with his criticism, a serious sin in the eyes of House veterans who were weaned on Sam Rayburn's advice: "To get along, go along."

The Orange County Republican wrote a scathing piece for Human Events, the conservative journal, that attacked the entire Congress for the way it had handled the transportation bill.

"Informed debate and factual exposition have been replaced by misinformation and chaos," Cox wrote. Then he went on to quote a friend, conservative humorist P.J. O'Rourke, who has referred to the U.S. Congress as a "Parliament of Whores." The allusion did not endear the Orange County congressman to the other lodgers at the bordello.

"That (was) not a way to make friends and influence people on that (public works) committee," Cox acknowledges. But "there's a 'get along, go along' M.O. there that I wasn't willing to cooperate with. And I thought I was reasonably polite . . . about the way I did it."

But critics, including some of his colleagues, see it differently. Several top congressional staffers, who were unwilling to be named, said that they see in Cox a certain aloofness, an unwillingness to accept the traditional Washington ways, that they believe borders on arrogance.

Cox's Harvard degrees, his earnest good looks, and his habitually impeccable appearance (white shirt, red tie, dark business suit) do not dispel the impression of a man that Marshall McLuhan might have described as terminally cool.

The congressman is meticulous in professional matters as well. When he wanted to augment the congressional salary of his first chief of staff (and former law school classmate) Robert Sutcliffe by also retaining Sutcliffe as a legal adviser to his campaign organization, Cox sought--and received--an authorizing letter from the House ethics committee.

And he took pains to secure and keep readily available copies of his Selective Service records, which show that he gave up a college deferment during the Vietnam War, but drew a lottery number sufficiently high to avoid induction.

"The one thing you have to keep in mind about Congressman Cox is that he takes this job super seriously," said an aide to another Orange County congressman. "When a city in Orange County comes in and says, 'We need help with this project,' we say, 'What do you need?' What Cox will do is rewrite the entire proposal and tell them, 'This is how you ought to do it.' "